1. Technical Field
The present invention relates to a heat pump system in which natural media are employed. More particularly, the present invention relates to a heat pump system using natural media such as ammonia and carbon dioxide and simultaneously accomplishing the economical utility.
2. Description of Related Art
Recently there have been resolutions made at Montreal (Montreal Protocol) and Kyoto (Kyoto Protocol to the United Nations Framework Convention on Climate Change), of which the objective is the disuse or reduction of several types of refrigerant such as chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC) or hydrofluorocarbon (HFC), in order to prevent the ozone layer destruction around the earth or Global Warming. In Japan, CFC, HCFC and HFC are collectively abbreviated as xe2x80x9cflonxe2x80x9d gas, respectively referred to as xe2x80x9cspecified flon,xe2x80x9d xe2x80x9cdesignated flonxe2x80x9d and xe2x80x9calternative flon,xe2x80x9d and their restriction is now under development. CFC has become disused in the end of 1995. HCFC is scheduled to become disused in 2020. Further, the emission of HFC into the atmosphere has become strongly limited. Consequently, it is has become necessary for the heat pump systems in refrigerating or air conditioning installations to use natural media (working fluid) such as ammonia, carbon dioxide, air or water.
The use of ammonia, however, is in many cases restricted due to its toxicity. For example, when ammonia is used for a refrigerator circuit having an evaporator incorporated in a showcase of supermarket or an air conditioning equipment of hotel, since unspecified individuals would visit there, there arises the difficulty of assuring safe and economical use of ammonia.
On the other hand, when carbon dioxide gas is used as the medium, because of its low critical temperature (31.1xc2x0 C.) and high saturation pressure at normal temperature (for example, about 75 kg/cm2 (abs) at 31.1xc2x0 C.), carbon dioxide has the disadvantageous point of ineffectiveness when used for air conditioning refrigerant of which evaporation temperature is relatively high. Further, where a compressor is required in order to overcome the problem discussed above, the related apparatus or instruments should be provided with strong pressure durability, consequently the system would become heavier and much expensive. Accordingly, although it has been theoretically possible to provide with an innovative heat pump system such as a dual phase refrigerating system utilizing ammonia and carbon dioxide, since the actual use would incur the problems of heavy weight and high cost, this type of heat pump system is not used in practice.
In the light of technical background and problems as above discussed, it is an object of the present invention to provide a heat pump system capable of cooling (refrigerating) and heating, by using a combination of ammonia and carbon dioxide. Further, since it is known that both ammonia and carbon dioxide are the natural media, existing in the natural environment and are organically recyclable, it is another object of the present invention to provide a heat pump system, which settles the problems of the toxicity in regard to ammonia as well as the high critical pressure at normal temperature in regard to carbon dioxide, and simultaneously to achieve sufficient utility at a lower cost.
To achieve the objects mentioned above, there is provided a heat pump system which utilizes a combination of an ammonia cycle and a carbon dioxide cycle carrying out refrigeration or heating, by combination of an ammonia cycle using ammonia as the medium and a carbon dioxide cycle using carbon dioxide as the medium. The natural circulation is done in the carbon dioxide cycle without incorporating a compressor.
With this structure, since it is not necessary to incorporate a compressor in the carbon dioxide cycle in order to circulate the carbon dioxide medium, less load power is required, and there is no need for using a large-size pressure vessel, and thus the heat pump system can be provided at a lower cost.
In addition to the elements, as discussed above, the circulation of carbon dioxide medium without incorporating the compressor is achieve, by natural circulation due to the difference of fluid heads of carbon dioxide media in the carbon dioxide cycle, and also by circulation due to heating or cooling of a part of the carbon dioxide cycle.
With this structure, in addition to the natural circulation realized by utilizing the difference of fluid heads, since the carbon dioxide medium is circulated by heating or cooling of a part of the carbon dioxide cycle, the operation can be made reliably and efficiently.
In addition to the elements as discussed above, the carbon dioxide cycle comprises a carbon dioxide refrigeration cycle functioning during cooling and a carbon dioxide heating cycle functioning during heating. The carbon dioxide refrigeration cycle is provided with an evaporator for carrying out the desired refrigeration by vaporizing carbon dioxide, at a position lower than a cascade condenser provided for carrying out cooling and liquefying the carbon dioxide medium. The carbon dioxide heating cycle is provided with a radiator for carrying out the desired heating by condensing carbon dioxide and also serving as the evaporator during refrigeration, at a position higher than a heat absorbing device provided for carrying out heating and vaporizing of carbon dioxide medium. The circulation of carbon dioxide medium in the carbon dioxide cycle is done, by means of cooling and liquefying the carbon dioxide medium in the carbon dioxide refrigeration cycle by the cascade condenser through which the ammonia cycle circulates during refrigeration, and by means of heating and vaporizing the carbon dioxide medium in the carbon dioxide heating cycle by the heat absorbing device during heating.
With this structure, the cascade condenser, as well as the evaporator and radiator serving for the desired refrigeration and heating in the carbon dioxide cycle, may be prepared by using tube or plate.
In addition to the elements as discussed above, the structural elements of the ammonia cycle are placed away from the evaporator or radiator carrying out the desired refrigeration and heating.
With this structure, since the structural elements of the ammonia cycle is placed away from the device carrying out the desired refrigeration and heating, such as on a roof or at any other outdoor space, the safety of the system can be secured.
In addition to the elements as discussed above, a fluid pump is provided for secondarily supporting the circulation of carbon dioxide medium in the carbon dioxide cycle.
With this structure, as compared with a (sensible heat using type of) brine chiller serving the same purpose by using ammonia as a refrigerant, the circulation of carbon dioxide medium can be supported by a considerably smaller amount of load power of the fluid pump, thereby reliable circulation of carbon dioxide medium can be secured.